Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$53.85	10.287%	$59.3895	$59.39	$59.40	$59.40
Purchase #2	$41.90	8.544%	$45.4799	$45.48	$45.50	$45.50
Purchase #3	$119.33	13.460%	$135.3918	$135.39	$135.40	$135.40
Purchase #4	$37.81	11.558%	$42.1801	$42.18	$42.20	$42.20
Purchase #5	$212.72	9.199%	$232.2881	$232.29	$232.30	$232.30
Purchase #6	$89.78	9.250%	$98.0847	$98.08	$98.10	$98.10
Purchase #7	$34.78	6.406%	$37.008	$37.01	$37.00	$37.00
7 purchase totals =	$590.17		$649.8221	$649.82	$649.90	$649.90